1. Field of the Invention
This invention relates to a process for selectively forming an organic film, and a process for selectively controlling the orientation of that organic film. In addition, this invention relates to an optical waveguide, a multilayer optical circuit, an electrical wiring and a TFT. In addition, this invention relates to an optical waveguide, a multilayer optical circuit, an electrical wiring that are formed using the above-mentioned organic film forming process.
2. Description of the Related Art
As an example of a process for manufacturing an organic film wherein an optical waveguide is formed, a process is known wherein an organic film is formed on a substrate using spin coating, this organic film is etched using reaction ion etching and patterned into the form of an optical waveguide.
In order to improve the performance of non-linear optical materials and other organic functional materials, it is necessary to control the orientation of an organic film grown on a substrate. In the past, oriented film coating has been realized within the substrate surface of a diacetylene thin film by a rubbing film. (J. S. Patel et al., Applied Physics Letters 56, 131(1992); T. Kanetake et al., Applied physics Letters 51, 1957 (1987)).
Optical circuits are playing important roles in various types of optical systems including optical interconnection of computers and optical exchanges. An example of an optical circuit of the prior art is indicated in FIG. 17. This optical circuit performs transmission of signals by coupling the IC with optical waveguides.
In the case of forming an organic film using spin coating, forming this organic film into a pattern and forming it into the form of an optical waveguide, light scattering tends to occur easily due to the rough edges of the patterned organic film. In addition, this type of formation also has the problem of etching processing of the organic film of a thickness on the micron order requiring considerable time.
Although waveguide formation by optical polymerization presents few problems in terms of light scattering, this type of formation has problems including the materials being limited and control of molecular orientation being difficult.
In the case of forming non-linear optical waveguides, it is desirable to orient the lengthwise axial direction of the molecules that form the vaveguide in the direction of polarization of the light. However, the above-mentioned processes of the prior art have the problem of molecular orientation being random. In the case of forming an electrical wiring using conductive organic materials as well, it is also desirable to make the orientation of molecules in the wiring uniform. Although orientation by drawing is also considered, since this is limited to cases wherein the base substrate is soft and there is the risk of defects occurring in the film, it is not a suitable process for manufacturing of devices.
Moreover, in the case of coupling an optical waveguide and an opto-electronic device, it is necessary to improve the adhesion between the two. However, the processes of the prior art had the problem of a gap tending to form easily between the device and the waveguide.
In addition, oriented film coating by a rubbing film has problems including those with respect to the flatness of the film, and the incorporation of a mechanical rubbing step in manufacturing processes of various photonics devices is itself not preferable. Although it is possible to control orientation by using organic single crystal for the substrate, due to the tremendous restrictions on the substrate, it is difficult to apply this to practical integrated devices.
In addition, with respect to optical circuits, as the number of IC increase and connections become increasingly complex, it is necessary for the waveguides to frequently intersect. In addition, it also becomes important to provide smooth interfaces between semiconductor lasers and photodiodes. Moreover, when optical switch and optical modulator functions are attempted to be demonstrated with waveguides, it becomes necessary to use non-linear optical materials. Normally, due to the large optical loss associated with non-linear optical waveguides, it is desirable to suppress the minimum length required for switching and wire the other portions with low-loss passive waveguides, thus making the multi-layering of optical circuits desirable.